Electrolytic bath for the removal of metals

ABSTRACT

Electrolytic bath for removing metallic coatings, such as nickel, chromium, zinc, tin, copper, cadmium or silver plate, from steel parts. The bath contains, in aqueous solution, nitric acid and/or its salts with inorganic and/or organic bases, organic acids and/or their salts and a watersoluble halogen compound, and is characterized in that the halogen compound is a soluble iodine compound.

United States Patent [191 Mietens et a1.

[ ELECTROLYTIC BATH FOR THE REMOVAL OF METALS [75] lnventors: Gerhard Mietens, l-lurth-Efferen;

Michael Ahlgrim, Erftstadt, both of Germany [73] Assignee: Hoechst Aktiengesellschalt, Cologne,

I Gennany' [22] Filed: Dec. 17, 1974 21 Appl. No.: 533,719

[30] Foreign Application Priority Data Dec. 20, 1973 Germany 2363352 [52] [1.8. CI. 204/146 [51] Int. Cl. C25F 5/00 [58] Field o[Search.. 204/146, 140, 129.75, 129.95

[56] References Cited UNITED STATES PATENTS 2,371,529 3/1945 Loose 204/146 [451 Oct. 14,1975

2,581,490 1/1952 Larsen 204/146 3,151,049 9/1964 Hendry 204/146 3,819,494 6/1974 Fountain 204/146 Primary Examiner-T. M. Tufariello Attorney, Agent, or Firm-Connolly and Hutz [57] ABSTRACT 13 Claims, No Drawings ELECTROLYTIC BATH FOR THE REMOVAL OF METALS The present invention relates to an electrolytic bath for removing metallic coatings, such as nickel, chromium, zinc, tin, copper, cadmium or silver plate, from steel parts, the bath containing, in aqueous solution, nitric acid and/or its salts with inorganic and/or organic bases, organic acids and/or their salts, and a watersoluble halogen compound.

The removal of an electro-deposited metal plating from steel becomes necessary, for example in those cases in which the plating is defective or in which it is desirable for it to be removed selectively. Elektrolytic baths are also used for the maintenance and cleaning of frames which clampingly receive the articles to be electro-plated. The electro-deposition of metals normally also causes the deposition of layers of .various metals on those parts of the frame which are in contact with the articles to be electro-plated. Needless to say it is necessary for those metal layers to be removed mechanically at regular intervals to provide for the necessary reliable passage of current to the workpiece.

Various baths of different composition have already been described in this field. German published Specification Offenlegungsschrift l 963 415, for example, describes an electrolytic demetallizing bath containing amines, nitrates, organic acids and water-soluble chlorine compounds. I

A further electrolytic bath has been described in German published Specification Offenlegungsschrift 2 146 828, consisting substantially of amines, nitrates, organic acids and water-soluble bromine compounds.

The above baths contain amines or aminoalcohols, especially those which have up to carbon atoms. The amines include primary, secondary and tertiary amines, such as trimethylamine, diethyland triethylamines, ethylene triamines, mono-, diand triethanol.

amines. Use is more particularly made in the above baths of the neutralization product of triethanolamine and nitric acid.

The organic solvents used in the above baths are formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, lactic acid and citric acid, or the alkali metal and/or ammonium salts thereof.

Highly water-soluble chlorine or bromine compounds, such as ammonium chlorides or bromides, hypobromites and bromates of alkali metals or ammonium, are further bath constituents.

The chlorine or bromine compounds are accelerators necessary to effect the removal of metal layers, particularly semi-polished nickel, within a reasonable period of time. On the other hand, they are activators of considerably increased corrosiveness for the base metal. Needless to say, it is practically impossible completely to inhibit corrosion of the base material, in an anodicelectrolytic operation.

It is highly desirable, however, for the corrosion of the base material to be minimized. To this end, at tempts have been made in the art to use the accelerator compounds in minor proportions and to substitute bromine compounds for the chlorine compounds.

In this manner, it is in fact possible slightly to reduce the corrosion of the base metal. On the other hand, however, the baths so made are in no way satisfactory bearing in mind that the minor proportions of chlorine and bromine compounds therein are difficult to control and regulate.

[t is accordingly an object of the present invention to provide an electrolytic demetallization bath which compares favorably with prior art baths in enabling metallic coatings, especially semi-polished nickel coatings, to be rapidly removed from steel articles, in being considerably less corrosive for the base metal, and in having a composition which is easier to control and regulate.

The object of the present invention can unexpectedly be achieved with the use ofa bath, wherein the halogen compound is a soluble iodine compound, preferably an iodide.

Very good results are produced with the use of baths containing from 0.05 up to 1.0 g/l, preferably from 0.4 up to 0.6 g/l, of iodine, dissolved as iodide, for example an alkali metal or ammonium iodide.lt is even more preferable for the baths to contain difficultly soluble iodine compounds, e.g. copper-l-iodide. It is good practice to use baths containing the difficultly soluble iodine compounds in a total proportion greater than that which corresponds to the solubility of the particular compounds in the baths so that the iodine compounds partially appear as solid phase material therein.

The baths of the present invention contain, as further known constituents, nitric acid and/or its salts with an alkali metal hydroxide or ammonium hydroxide or with an aliphatic amine or aminoalcohol or a blend of these salts, in proportions within the range 15 and 60 g/l, as well as organic acids, such as formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, lactic acid or citric acid, or blends thereof, their salts or salt blends, in preferred proportions within the range 10 and 40 g/l.

It is also advantageous to establish a pH-value ranging from 6.5 to 7.5 in the baths ofthe present invention.

It is possible for the difficultly soluble iodine compounds to be used in the form of solid phase material lying on the bottom of the bath, or to be placed in anode bags, for example, which'are suspended from a holder and continually contacted with the electrolyte. The electrolytic demetallization being critically determined by the addition of the halogen compound, it is absolutely necessary to avoid overfeeding of the bath with halogen. To this end, use is made of difficultly soluble iodine compounds, e.g. copper-I-iodide, which produce a bath wherein the iodine content need not be controlled analytically. Overfeeding with iodine is practically excluded as the bath having the difficultly soluble iodine compounds therein is a self-controlling demetallization bath which is easy to handle.

Baths containing soluble iodine compounds enable metal coatings to be removed from steel at least as rapidly as with the use of analogous baths containing chlorine or bromine compounds, and they combine this with considerably reduced corrosiveness for the steel itself.

Baths containing readily and difficultly soluble chlorine and bromine compounds, respectively, and baths containing difficultly soluble iodine compounds are compared with each other hereinafter.

EXAMPLE I The basic electrolyte was composed of: g/l of triethanolamine, 48 g/l of HNO of 63 strength, and

20 g/l of NH -acetate.

Chloride Bromide Iodide Iodide (NaCI) (KBr) (CuJ) (KJ) 0.1 g/l 7.1 mg 4.1 mg 3.3 mg 2.0 mg 1.0 g/l 420 mg 4! mg 5 mg 6.9 mg 5.0 g/l 2420 mg I723 mg 210 mg 801 mg 10.0 g/l 4010 mg 2870 mg 268 mg 2455 mg As can clearly be seen, the above material underwent considerably less corrosion upon the use of difficultly soluble iodine compounds which were found to confer self-controlling properties to the demetallizing electrolyte.

EXAMPLE 2 The basic electrolyte and the electrolytic conditions were the same as those used in Example 1, save that the base material was stainless steel (material No. I4 571 (German Industrial Standard X CrNiMoTi 1810)).

Quantity of steel removed per hour of electrolytic operation upon the addition of:

Chloride Bromide Iodide (NaCl) (KBr) (CuJ) 0.! g/l 7.3 mg 8.4 mg 4.3 mg 5 g/l I74 mg ISI mg 34 mg l0 g/l 272 mg 291 mg 38 mg It can clearly be seen that difficultly soluble Cu] is of considerably reduced corrosiveness for stainless steel.

We claim:

1. Electrolytic bath for removing metallic coatings, such as nickel, chromium, zinc, tin, copper, cadmium or silver plate, from steel parts, the bath containing, in aqueous solution,

a. at least one substance selected from the group consisting of nitric acid and its salts with inorganic and organic bases;

b. at least one substance selected from the group consisting of organic acids and their salts; and

c. a water-soluble halogen compound, being characterized in that the halogen compound is a soluble iodine compound.

2. The bath as claimed in claim 1, containing between 0.05 and 1.0 g/l of iodine in the form of dissolved iodide.

3. The bath as claimed in claim 2, containing between 0.4 and 0.6 g/l of iodine in the form of dissolved iodide.

' 4. The bath as claimed in claim 1, containing an alkali metal or ammonium iodide as the iodine compound.

5. The bath as claimed in claim 1, containing a diff!- cultly soluble iodine compound.

6. The bath as claimed in claim 5, containing copper- I-iodide as the difficultly soluble iodine compound.

7. The bath as claimed in claim 5, containing the difficultly soluble iodine compound in a total proportion being greater than that which corresponds to the solubility of the iodine compound in the bath, so that the iodine compound partially appears as solid phase material therein.

8. The bath as claimed in claim 1, containing the nitric acid in the form of its salts with an alkali metal hydroxide or an ammonium hydroxide or an aliphatic amine or aminoalcohol, or a blend of these salts.

9. The bath as claimed in claim 1, containing the nitric acid salts in proportions within the range 15 and 60 g/l.

10. The bath as claimed in claim 1, containing an organic acid being selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, lactic acid or citric acid.

1 l. The bath as claimed in claim 1, containing at least one salt of an acid being selected from the group consisting of formic acid, acetic acid, propionic acid, 0xalic acid, malonic acid, lactic acid or citric acid.

12. The bath as claimed in claim 1, containing the organic acid or its salts in proportions within the range 10 and 40 g/l.

13. The bath as claimed in claim 1, having a pH-value between 6.5 and 7.5.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIUN PATENTNO. 3 912 603 DATED October 14, 1975 lN\/ ENTOR( I Gerhard Mietens et a1.'

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the cover sheet first column please change Assignee "Hoechst Aktiengesellschaft, Cologne, Germany" to --Hoechst Aktienge-sellschaft, D 623 Frankfurt/Main-80, Federal Republic of Germany- Signed and firalcd rhe twenty-second Day 0? June 1976 [SEAL] A nest:

RUTH C. MASON I C. MARSHALL DANN A! I 8 fficer ('ommissioner nflazenrs and Trademarks 

1. ELECTROLYTIC BATH FOR REMOVING METALLIC COATINGS, SUCH AS NICKEL, CHROMIUM, ZINC, TIN, COPPER, CADIUM OR SILVER PLATE, FROM STEEL PARTS, THE BATH CONTAINING, IN AQUEOUS SOLUTION, A. AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID AND ITS SALTS WITH INORGANIC AND ORGANIC BASES, B. AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF ORGANIC ACIDS AND THEIR SALTS, AND C. A WATER-SOLUBLE HALOGEN COMPOUND, BEING CHARACTERIZED IN THAT THE HALOGEN COMPOUND IS A SOLUBLE IODINE COMPOUND.
 2. The bath as claimed in claim 1, containing between 0.05 and 1.0 g/l of iodine in the form of dissolved iodide.
 3. The bath as claimed in claim 2, containing between 0.4 and 0.6 g/l of iodine in the form of dissolved iodide.
 4. The bath as claimed in claim 1, containing an alkali metal or ammonium iodide as the iodine compound.
 5. The bath as claimed in claim 1, containing a difficultly soluble iodine compound.
 6. The bath as claimed in claim 5, containing copper-I-iodide as the difficultly soluble iodine compound.
 7. The bath as claimed in claim 5, containing the difficultly soluble iodine compound in a total proportion being greater than that which corresponds to the solubility of the iodine compound in the bath, so that the iodine compound partially appears as solid phase material therein.
 8. The bath as claimed in claim 1, containing the nitric acid in the form of its salts with an alkali metal hydroxide or an ammonium hydroxide or an aliphatic amine or aminoalcohol, or a blend of these salts.
 9. The bath as claimed in claim 1, containing the nitric acid salts in proportions within the range 15 and 60 g/l.
 10. The bath as claimed in claim 1, containing an organic acid being selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, lactic acid or citric acid.
 11. The bath as claimed in claim 1, containing at least one salt of an acid being selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, lactic acid or citric acid.
 12. The bath as claimed in claim 1, containing the organic acid or its salts in proportions within the range 10 and 40 g/l.
 13. The bath as claimed in claim 1, having a pH-value between 6.5 and 7.5. 